The manufacture of a surfactant composition typically produces, in addition to the desired end product, numerous residual products which can adversely affect the efficacy of the surfactant component. Such a manufacture will typically produce a host of undesirable by-products along with substantial amounts of reactant solvent excesses required for the manufacture. These residual products will normally have a deleterious effect upon surfactant functionality even though they may be present in very small or trace amounts.
The inherent functional attributes of the surfactant composition makes it extremely difficult and costly to effectively remove residual contaminants from such surfactant compositions. Consequently, surfactant manufacturers are often placed in the position to sacrifice optimal surfactant efficacy because of manufacturing difficulties and the cost considerations involved in attempting to remove such adverse contaminants from surfactant compositions.
Fatty alcohols (e.g. C.sub.8 -C.sub.22 straight, branched, saturated or unsaturated, aliphatic alcohols) are extensively used as a reactant in the manufacture of surfactants. These fatty alcohols are typically reacted with a hydrophilic reactant at the appropriate molar ratios to impart the desired hydrophilic lipophilic balance (H.L.B.) to the desired surfactant composition. Residual levels of these fatty alcohols often remain as an undesirable contaminant of the manufactured surfactant composition.
The prior art has proposed a variety of means for removing such nonfunctional and deleterious residues from surfactant compositions. Extraction with complex solvent systems, washing, phase separation, distillation, centrifugation, etc. are included among the removal proposals. Although these proposed techniques may be used to partially remove residual contaminants from surfactant compositions, such methods are relatively ineffective when it is desired to remove relatively small amounts (e.g. two percent or less) of residual contaminants therefrom.
The difficulty and complexity, equipment and capital investments, energy, production of adverse decompositional by-products, labor and time, etc. considerations usually outweigh the anticipated removal benefits. The removal problem becomes particularly acute at residual contamination levels of less than 1% by weight of the active surfactant weight.
Consequently, the surfactant manufacture is typically forced into a position of leaving the residues within the surfactant composition in order to retain cost-competitive position with other functionally related surfactant compositions. The chemical and/or physical degradation of the active surfactant component arising from the removal of such residual contaminants often yield products of a substantially lower surfactant efficacy than the unrefined surfactant composition.
U.S. Pat. No. 2,663,426 issued Dec. 22, 1953 to Wilson et al discloses a process for purifying water-soluble alcohols contaminated with odorous, high-boiling hydrocarbons and sulphur compounds which arise as a result of manufacture via the hydration of mono-olefins. The Wilson et al process involves treating lower alkyl (C.sub.1 -C.sub.5) alcohols with sand to remove the malodorous contaminants therefrom.
A patent by Cahill (U.S. Pat. No. 2,913,501 issued Nov. 17, 1959) discloses chromatographically purifying crude fatty alcohols. Cahill discloses that the fatty alcohol solution typically contains about two to fifty percent by weight impurities comprised of fatty hydrocarbons, fatty esters and fatty ethers.
Cahill then dissolves the crude alcohol in a petroleum ether and selectively adsorbs, with an activated alumina adsorbent, fatty ethers, esters and alcohols (e.g. see column 3, lines 24-34). The fatty hydrocarbon impurities remain in said solution with the petroleum ether. Cahill washes the adsorbed fatty ethers, esters and alcohols with petroleum ether to elute the fatty ethers from the adsorbent, then treats the adsorbent containing adsorbed fatty esters and alcohols with benzene or carbon tetrachloride solution to effectuate selective elution of the fatty esters. An ethanol wash is then used to elute the fatty alcohol from the adsorbent.
The petroleum industry has heretofore extensively used porous adsorbents in the manufacture of hydrocarbon products. Certain of the adsorbents possess the ability to function as sieves on a molecular scale. Such sieves, commonly referred to in the art as molecular sieves, are commercially available in a host of different forms. Molecular sieves, such as the crystalline zeolites, have been used to remove water and other polar compounds from hydrocarbon streams, to fractionate isomers and as a catalyst under conditions wherein the reactant or a reaction mixture is selectively sorbed into the pores of the molecular sieve and catalytically converted into the desired end product.
Crystalline zeolites, natural or synthetic, are chemically composed aluminosilicate minerals containing some group I or II elements. Zeolites are commercially important for their molecular sieving effects. The pore sizes of the crystalline latice is modified slightly by the cationic exchange after the synthesis of the molecular sieve. The early zeolite forms exhibited strong water adsorbent factors and, accordingly, were primarily used as adsorbents for polar compounds such as water. Molecular sieves which selectively adsorb hydrophobic molecules have been more recently introduced to the trade. These hydrophobic zeolites possess a highly uniform crystalline latice and may be effectively utilized as selective adsorbents for separating hydrocarbon isomeric mixtures in which the separated isomers may only differ in molecular size of 0.2 angstroms or less. These materials are often referred to as small pore hydrophobic adsorbents or zeolites. Characteristically, these adsorbents possess an intercrystalline sorption capacity for n-hexane far greater than that for water and thus exhibit hydrophobic properties.
Representative patents disclosing the preparation, characteristics and typical industrial applications of these hydrophobic zeolites include U.S. Pat. Nos. 4,309,281 issued Jan. 5, 1982 to Dessau, 3,699,182 issued Oct. 17, 1972 to Cattanach, 3,702,886 issued Nov. 14, 1972 to Argauer et al, 4,061,724 issued Dec. 6, 1977 to Grose et al and 4,277,635 issued July 7, 1981 to Oulman et al. The Dessau patent teaches that hydrophobic zeolites have an unusually low alumina content, i.e. high silica to alumina ratio. The hydrophobic zeolites reportedly retain their crystallinity even after prolonged exposure to steam, high temperatures and pressures. Cattanach discloses selective adsorption of p-xylene from m-xylene dispersed in a fluid carrier by contacting isomeric mixtures thereof with a hydrophobic zeolite.
U.S. Pat. No. 3,702,886 issued Nov. 14, 1972 to Argauer et al discloses a method for preparing these hydrophobic, crystalline aluminosilicate zeolites and their use in the catalytic cracking of hydrocarbon stocks at 560.degree. F.-1100.degree. F. and operative pressures ranging from subatmospheric to several hundred atmospheres. A publication entitled "An Evaluation of Adsorption Properties of Silicalite for Potential Application to Isolating Polar Low-Molecular-Weight Organics from Drinking Water" by Chriswell et al (National Technical Information Service, U.S. Department of Commerce, Springfield, Va., 22161, PB 83-148502) mentions that silicalite (a hydrophobic sorbent) can be used to accumulate small organic species (e.g. phenol, benzene, propanol and hexane) from aqueous solutions while conventional molecular sieves are used to accumulate water from organic solvents.
Further information relating to such hydrophobic sorbents include an article entitled "Reactions on ZSM-5-Type Zeolite Catalysts" by J. R. Anderson et al Journal of Catalysis 58, 114-130, (1979); "Para-Directed Aromatic Reactions Over Shaped Selective Molecular Sieve Zeolite Catalyst" by N. Y. Chen, Journal of American Chemical Society, 101:22, Oct. 24, 1979; a preprint of an article presented to the American Institute of Chemical Engineers, Spring 1983 meeting, Houston, Tex., Mar. 27-31, 1983 entitled the "Adsorption of Ethanol and Water Vapors by Silicalite" by S. M. Klein and W. H. Abraham; a trade bulletin entitled "Union Carbide Molecular Sieves, Molecular Sieves Catalyst", etc.
Studies by Chriswell et al upon gas phase adsorption of silicalite mention a high gas distribution coefficient on unbound silicalite at 200.degree. C. The author's primary concern involves the removal of trace amounts of relatively small molecular weight organics from drinking water.
Further information pertaining to these hydrophobic zeolites may be obtained by reference to numerous trade publications and other information bulletins (e.g. see Nature 271, Feb. 9, 1978, pp. 512-517, etc.). Commercially available small pore hydrophobic adsorbents include ZSM-5 manufactured by the Mobil Oil Corporation and Silicalite S-115 manufactured by Union Carbide Corporation. The most commonly available forms of these hydrophobic zeolites are presently reported to possess an open pore structure and contain a multiplicity of channels measuring six angstroms in diameter (.+-.0.2A) that occupy approximately one-third of the total crystal volume. Their decompositional temperatures are reported to exceed 1100.degree. C., and they are stable in the presence of most solvents and corrosives including strong acids and oxidizing agents. Other synthetic hydrophobic zeolite forms with a uniform channel structure of differing molecular dimensions have also been reported by the art.
Adsorption techniques relying upon other different types of sorbents have also been proposed. U.S. Pat. No. 2,556,248 issued June 12, 1951 to Amick discloses an aqueous process for purifying ethers by distillization and adsorption with silica gel. According to Amick the water and lower alkyl alcohol impurities remain with the solvent system while the lower alkyl ether is absorbed by the silica gel. U.S. Pat. No. 3,565,885 issued Feb. 23, 1971 to Molotsky et al disclose a process for preparing color stable glycosides. Molotsky et al proposes the use of a strongly basic anionic exchange resin (hydroxy form or weakly anionic form other than phenolic-formaldehyde based resins) to remove adverse color-producing bodies such as reducing sugars from lower alkyl glycoside mixtures.
The inventor herein was confronted with a problem of removing relatively small amounts (e.g. 2% or less) of fatty alcohol and fatty by-product residues from surfactant compositions. The inventor recognized that the prior methods became progressively ineffective as the concentration of fatty alcohol and by-product contaminants within the surfactant composition became more diluted (1% or less). The problems associated with the removal of lipophiles from surfactant compositions are much more difficult and complex than those customarily encountered in most purification processes. These problems are compounded by the uniquely different and inherent properties of the surfactant component and its tenacious associative effect upon lipophilic contaminants within the surfactant composition. A unique process permitting the surfactant manufacturer to effectively remove such residual contaminants without degrading the surfactant component would significantly enhance the overall efficacy of the surfactant composition. Such a process would be particularly useful if it could be accomplished on a cost-effective basis.
Throughout the specification, percentages and ratios are by weight, pressures are atmospheres over ambient and temperatures are in degrees Celsius unless otherwise indicated.